Yig filter having a single substrate with all transmission line means located on a common surface thereof

ABSTRACT

One or more non-overlapping transmission line conductors fabricated on one planar surface of a single slab of an electric material mounted on a ground plane. At least one YIG resonator element is located in a cavity formed in the surface of the substrate facing the ground plane. The YIG resonator element, moreover, is positioned in close proximity to said one or more transmission line conductors a selected distance below the outer surface of the substrate and below the transmission line circuitry.

United States Patent 1 1 Moore et al.

[ June 19, 1973 YIG FILTER HAVING A SINGLE SUBSTRATE WITH ALLTRANSMISSION LINE MEANS LOCATED ON A COMMON SURFACE THEREOF [75]Inventors: Robert A. Moore, Severna Park;

Theodore M. Nelson, Catonsville,

both of Md.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: Aug. 17, 1970 [21] Appl. No.: 64,361

[52] US. Cl. 333/73 R, 333/76, 333/84 M [51] Int. Cl. HOlp 3/08, H03h7/08 [58] Field of Search... 3-33/73 R, 24.1, 24.2,

[56] References Cited UNITED STATES PATENTS 3,448,409 6/1969 Moose et al333/84 M 3,585,531 6/1971 Degenford et al.... 333/10 x 3,417,294 12/1968Steidlitz 333/84 x 3,022,470 2/1962 Oliner 333/24.2x 3,102,244 8/1963Seidel 333/24 2 3,458,837 7/1969 Ngo 333173 OTHER PUBLICATIONS Lewin AResonance Absorption lsolator," in Microstrip for 4GC/S Proceedings oflEE Part B Supplement 1957; Title Page & pp. 364-365.

Ferrites Can be Replaced With Yttrium Iron Garnet, in Electronic Design,Aug. 6, l958, single page. Matthaei, Magnetically Tunable Band-StopFilters, in IEEE Transactions on Microwave Theory and Techniques, March,1965; pp. 203-212.

Barret Microwave Printed Circuits-A Historical Survey, in IRETransactions on Microwave Theory and Techniques, March, 1955; Cover Pageand pp. l-7 Mariner Introduction to Microwave Practice Aca demic Press,Inc., New York, 1961; Title Page & pp. 33-35.

Primary ExaminerRudolph V. Rolinec Assistant Examiner-Marvin NussbaumAtt0rneyF. H. Henson, E. P. Klipfel and J. L. Wiegreffe [57] ABSTRACTOne or more non-overlapping transmission line conductors fabricated onone planar surface of a single slab of an electric material mounted on aground plane. At least one YlG resonator element is located in a cavityformed in the surface of the substrate facing the ground plane. The YIGresonator element, moreover, is positioned in close proximity to saidone or more transmission line conductors a selected distance below theouter surface of the substrate and below the transmission linecircuitry.

l0'Claims, 11 Drawing Figures PATENTED JUN-1 3. 740 675 sum 2 or z errYIG FILTER HAVING A SINGLE SUBSTRATE WITH ALL TRANSMISSION LINE MEANSLOCATED ON A COMMON SURFACE THEREOF BACKGROUND OF THE INVENTION 1. Fieldof the Invention The present invention relates generally to magneticallytunable filters and more particularly to magnetically tunable bandpassand band stop filters which utilize ferrimagnetic resonators incombination with deposited or etched microstrip line conductors on adielectric substrate.

2. Description of the Prior Art The basic principles and theory ofoperation of ferrimagnetic resonators used as filters in waveguides,strip transmission lines and the like appears in a publication entitledDesign of Magnetically Tunable Microwave Filters Using Single CrystalYttrium-Iron-Garnet Resonators," by P. S. Carter, Jr. appearing in theIRE Transactions by Microwave Theories and Techniques, Volume MTT-9,pages 252-260 (May, 1961). Also reference is made to a text entitledMlcrowave Filters, Impedance-Matching Networks and Coupling Structures,George L. Matthaei, et al., McGraw-Hill, Inc., 1964, pp. 1043-1085,inclusive.

Ordinarily, strip transmission line YIG filters are comprised ofoverlapping or crossing strip transmission lines at right angles to eachother with a YIG sphere located between the transmission line at thepoint of overlap. If the point of overlap is an RF short circuit anda'magnetic field of the proper magnitude is applied to the YIG sphere atright angles to the two transmission lines, filtering and power limitingwill occur. Such apparatus is mentioned as being known prior art in U.S.Pat. No. 3,289,112 issued to Charles E. Brown. This patent, however,additionally discloses the concept of locating the YIG sphere beneaththe overlapping lines in a cavity of one of the dielectric wall membersinstead of between the overlapping striplines. The overlappingstriplines are printed on a pair of opposing dielectric wall members andthe two lines are peeled back and extended through one of the twodielectric wall members to a ground plane associated therewith in orderto form an RF short circuit for signals applied to the conductors. Whilethe Brown patent teaches a novel means of coupling two striplineelements to a single pole or resonator and has an advantage over certaintypes of YIG filters in that the YIG sphere need not be between the twocoupled lines, it has the disadvantage of most types of YIG filters inthat it is restricted to a single YIG sphere coupling both lines andtherefore only single pole filters can be realized by this technique.

SUMMARY OF THE INVENTION The present invention is an improvement inapparatus ofthe type referred to above and is particularly suitable forfabrication into integrated circuitry. In the present invention a singleor multi-pole YIG filter is disclosed which comprises a singledielectric substrate mounted on a ground plane so that its inner face iscontiguous with one surface of the ground plane. One or morenon-overlapping microstrip line conductors are fabricated on the outerface of the substrate and terminate at input and output couplers ofelectromagnetic energy located at the edges of the substrate. A selectednumber, one or more, YIG resonator elements are located in a cavityformed. in the inner face of the substrate so that said selected numberof resonator elements are positioned beneath the outer face in closeproximity to said one or more line conductors. A magnetic field isapplied substantially orthogonal to the outer face to tune said selectednumber of YIG resonators to provide a predetermined filtering action ofelectromagnetic signals being transmitted between said input and outputcouplers.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a firstembodiment of the subject invention and being illustrative of a singlepole bandstop filter;

FIG. 2(a) is a fragmentary view of FIG. 1 taken along the line 22illustrating the location of a YIG sphere in the substrate;

FIG. 2(b) is a fragmentary view of FIG. 1 taken along the line 22illustrating a YIG disc resonator element mounted in the substrate;

FIG. 3 is a perspective view of a second embodiment, being illustrativeof a single pole filter having two noncrossing microstrip lineconductors on the outer face of the substrate;

FIG. 4 is a fragmentary view of the embodiment shown in FIG. 3 takenalong the line 4-4 illustrating the location of a YIG sphere in relationto the two microstrip line conductors;

FIG. 5 is a perspective view of a third embodiment of the subjectinvention being'illustrative of a two pole filter and including twomicrostrip line conductors fabricated on the outer face of the substrateand terminating in a short circuit thereon;

FIG. 6 is a fragmentary view of FIG. 5 taken along the line 66illustrating the location of two YIG resonators in relation to themicrostrip line conductors;

FIG. 7 is a perspective view of a fourth embodiment of the subjectinvention similar to the embodiment shown in FIG. 5;

FIG. 8 is a fragmentary view of the embodiment shown in FIG. 7 takenalong the line 8-8;

FIG. 9 is a partial cut away view of the embodiment shown in FIG. 7modified to embody a three pole YIG filter; and

FIG. 10 is a partial cut away view of the embodiment shown in FIG. 7modified to embody a four pole YIG filter.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2(a), asingle microstrip line conductor 10 is deposited or etched on the outerface 12 of a dielectric substrate 14 which may be comprised of forexample alumina, sapphire or some other ceramic material. The dielectricsubstrate 14 is mounted on a metallic ground plane 16 which iscoextensive with its inner face 18. The microstrip line conductor 10 isof a substantially constant width and thickness and extends betweenopposite edges of the dielectric substrate l4 terminating at each end inan electrical connector 20 and 22 which is adapted to coupleelectromagnetic energy to and from the line conductor 10. A cavity 24 isfabricated into the inner face 18 directly beneath the line conductor 10between the RF connectors 20 and 22. In the present embodiment thecavity 24 comprises a round dimple wherein a YIG sphere resonatorelement 26 is positioned so that it lies a predetermined distance, forexample 0.005 inches below the upper surface 12 of the substrate 14.Additionally, the inner face 28 of the ground plane 16 contains a recess30 including a dimple 32 for accepting the protrusion of the YIG sphere26 when it is of such a size relative of the thickness of the substrate14 that itwould otherwise prevent mating of the surfaces 18 and 28.

When RF signals are applied to the line conductor by means of theconnectors 20 and 22 and a DC biasing magnetic field H of the propermagnitude is applied to the YIG sphere 26 substantially orthogonal tothe line conductor 10, signals within a predetermined frequency rangewill not pass the point of the YIG sphere when it is at or near itspoint of resonance, thereby providing a bandstop filter. If for exampleRF energy is coupled into connector 20 only those frequencies which havebeen passed will exit at the other connector 22.

While it is desirable in certain applications to utilize a YIG sphere 28such as shown in FIG. 2(a) as the resonator element, it sometimesbecomes desirable to utilize a YIG resonator in the form of a disc whichis shown in FIG. 2(b) and identified by reference numeral 34. In theembodiment shown, the disc 34 has a diameter substantially equal to thecircular dimension of the cavity 25 and does not protrude below theinner face 18 of the substrate.

The second embodiment of the subject invention is shown in FIGS. 3 and4. It comprises a single pole bandpass or bandstop filter including apair of non-. overlapping microstrip line conductors 36 and 38 ofsubstantially equal width dimensions fabricated on the outer face 12 ofthe dielectric substrate 14 so that a portion of their respectivelengths run parallel to each other and then diverge into respective RFconnectors located at the edges of the substrate. More particularly,microstrip line conductor 36 runs diagonally across a portion of theouter face 12 terminating in the RF connectors 40 and 42 while lineconductor 38 also runs diagonally across the outer face 12 separatedfrom the other conductor 36 by predetermined separation and terminatingin respective RF connectors 44 and 46. Midway between the parallelportions of the two line conductors 36 and 38 is a selected number of,in this case one, YIG resonator elements shown as a YIG sphere 26located in the substrate 14 beneath the outer face 12. Rather than beinglocated directly beneath the line conductor 10 as shown in theembodiment in FIG. 1, the present embodiment locates the YIG sphere 26between the parallel line portions of the conductors 36 and 38. Byapplying a DC biasing magnetic field I-I through the YIG sphere 26selective coupling of electromagnetic energy occurs between the lineconductors 36 and 38 because of the resonance characteristic of the YIGsphere. This configuration is adapted to provide low insertion lossbandpass coupling between the transmission lines 36 and 38.

For minimum insertion loss bandpass transmission an RF short must beapplied at the location of the sphere 26. This can be provided in theembodiment shown in FIG. 3 for example, by external short circuits shownschematically by the reference numerals 41 and 45 directly connectedfrom the connectors 40 and 44, respectively, to the ground plane 16.When this is done input signals applied to one of the oppositeconnectors 42 or 46 will be coupled out of the other connector. Byselectively adjusting these short circuits for example by means ofsliding shorts, not shown, the effect of the short circuit will betransformed on each line 36 and 38 to a position adjacent the sphere 26wherein the tightest coupling will occur and best transmission effectswill result. It should be noted, however, when desirable the shortcircuits could be applied to connectors 42 and 46 and connectors 40 and44 utilized as the inputoutput ports for coupling between microstripline conductors 36 and 38.

A third embodiment of the subject invention is shown in FIGS. 5 and 6and comprises a first and a second microstrip line conductor 48 and 50fabricated on the upper face 12 of the substrate 14 and which terminatein a short circuit 52 also fabricated on the upper face 12. The firstline conductor 48 extends to one edge of the substrate 14 but turning ata substantially right angle inwardly of the edge to contact the shortcircuit 52. The second line conductor 50 extends to an adjacent edge ofthe substrate 14 and running in a substantially straight line to theshort circuit 52 but being substantially parallel to a relatively smallportion of the line conductor 48 in proximity to the short 52. A cavity54 is formed in the inner face 18 of the substrate 14 directly beneaththe portions of the line conductors 48 and 50 which are adjacent to theshort 52. A first and a second YIG resonator element 56 and 58 in theform of a sphere are located in the cavity 54 respectively beneath theline conductor 48 and 50 by means of the dimples 60 and 62 formedtherein. Both YIG resonator elements 56 and 58, however, do not contactthe respective line conductors but lie beneath the upper face 12 of thesubstrate 14 by predetermined separation. This separation wasillustrated in reference to the first embodiment described with respectto FIGS. 1 and 2(a). Additionally, the ground plane 16 includes a recess64 beneath the cavity 54 in order to accommodate a portion of the YIGresonator elements 56 and 58. Whereas the embodiment shown in FIGS. 3and 4 required four RF connectors, the third embodiment requires onlytwo connectors 66 and 68 respectively coupled to the extremities of theline conductors 48 and 50 which appear at the adjacent edges of thesubstrate 14. When RF signals are applied to line conductors 48 and 50by means of the RF connectors 66 and 68 and a DC biasing magnetic fieldH of proper magnitude is applied to the YIG resonator elements 56 and58, a two pole filter of the bandpass type will be provided andselective coupling between line conductors 48 and 50 will occur due tothe resonance phenomenon of the YIG resonator elements.

Referring now to FIGS. 7 and 8 there is illustrated a fourth embodimentof the subject invention which is similar to the embodiment shown inFIG. 5 with the exception that the electrical short 52 on top of thesubstrate 14 is deleted and the microstrip conductors 48 and 50 areterminated in a short near the YIG spheres 56 and 58 on the upper orinner face 28 of the ground plane 16. This is provided by the holes 49and 51 completely through the substrate 14. By a suitable metal platingprocedure the conductors 48 and 50 are extended into the holes 49 and51, respectively and an electrical contact made with the ground plane16. This is shown in greater detail in FIG. 8.

Although up to this point one and two pole YIG filters have beenconsidered, the present invention particularly as regards the lastembodiment shown in FIGS. 7 and 8 is adapted to be configured with threeor more poles or YIG resonators. For example, FIG. 9 discloses amodification of the embodiment shown in FIG. 7 to include three equallyspaced YIG resonators 56, 57, and 58 located in the recess 64 along arow transverse to the line conductors 48 and 50 under the surface 12 ofthe substrate 14. FIG. 10, on the other hand, illustrates a four poleYIG filter and includes four resonators 56, 58, 59 and 61 arranged in arow transverse to the line conductors 48 and 50;

What has been shown and described, therefore, is an improvement in YIGfilter apparatus requiring one substrate, and one ground plane with allof the microstrip line conductor means being located on a common surfaceor face in a non-overlapping fashion with the YIG resonator elementmeans being located in the substrate beneath the microstrip lineconductors.

We claim as our invention:

1. A magnetic tunable microstrip transmission line filter, comprising incombination:

a. dielectric substrate means having inner and outer faces;

b. ground plane means having inner and outer faces, said outer facethereof abutting the inner face of said dielectric substrate means;

c. first and second microstrip transmission line means for transmittingelectromagnetic wave energy located on said outer face of said substratemeans;

d. ferrimagnetic resonator means positioned to selectively couple saidelectromagnetic wave energy between said first and second microstriptransmission line means;

e. means for magnetically biasing said ferrimagnetic resonator means;wherein f. said first and second transmission lines includesubstantially equal parallel line portions and wherein said resonatormeans comprises at least one yttrium iron garnet sphere located in closeproximity to said parallel line portions.

2. The invention as defined by claim 1 wherein said sphere is locatedbetween said parallel line portions beneath said outer face of saiddielectric substrate means.

3. The invention as defined by claim 1 wherein said first and secondtransmission line means comprise first and second line conductors, and ashort circuit conductor contacting said first and second lineconductors, said first and second line conductors and said short circuitconductor being located in substantially a common plane on said outerface of said dielectric substrate means, and wherein said resonatormeans comprises at least one YIG resonator element located in closeproximity to said first and second line conductors.

4. The invention as defined by claim 3 wherein said at least one YlGresonator is located directly beneath at least one line conductor.

5. The invention as defined by claim 1 wherein said first and secondtransmission line means comprise first and second line conductors, and ashort circuit conductor contacting said first and second lineconductors, said first and second line conductors and said short circuitconductor being located in substantially a common plane on said outerface of said dielectric substrate means, wherein said resonator meanscomprises a plurality of YIG resonators located in close proximity tosaid first and second line conductors.

6. The invention as defined by claim 5 wherein said plurality of YIGresonators are comprised of a first and a second sphere of singlecrystal yttrium-iron-garnet respectively located beneath said first andsecond line conductors.

7. The invention as defined by claim 1 wherein said first and secondtransmission line means comprise first and second line conductorslocated in substantially a common plane on said outer face of saiddielectric substrate and passing through said dielectric means at apoint in proximity to said resonator means and respectively terminatingin an electrical short circuit on said outer face of said ground plane.

8. The invention as defined by claim 7 wherein said resonator meanscomprises at least one YIG resonator element located in close proximityto said first and second line conductor and said electrical shortcircuit.

9. The invention as defined by claim 7 wherein said resonator meanscomprises a plurality of YIG resonators.

10. The invention as defined by claim 9 wherein said plurality of YIGresonators comprises at least three YIG resonators arranged in a rowbeneath said outer face of said substrate substantially perpendicular tosaid first and second line conductor and within a boundary defined bysaid line conductors.

1. A magnetic tunable microstrip transmission line filter, comprising in combination: a. dielectric substrate means having inner and outer faces; b. ground plane means having inner and outer faces, said outer face thereof abutting the inner face of said dielectric substrate means; c. first and second microstrip transmission line means for transmitting electromagnetic wave energy located on said outer face of said substrate means; d. ferrimagnetic resonator means positioned to selectively couple said electromagnetic wave energy between said first and second microstrip transmission line means; e. means for magnetically biasing said ferrimagnetic resonator means; wherein f. said first and second transmission lines include substantially equal parallel line portions and wherein said resonator means comprises at least one yttrium iron garnet sphere located in close proximity to said parallel line portions.
 2. The invention as defined by claim 1 wherein said sphere is located between said parallel line portions beneath said outer face of said dielectric substrate means.
 3. The invention as defined by claim 1 wherein said first and second transmission line means comprise first and second line conductors, and a short circuit conductor contacting said first and second line conductors, said first and second line conductors and said short circuit conductor being located in substantially a common plane on said outer face of said dielectric substrate means, and wherein said resonator means comprises at least one YIG resonator element located in close proximity to said first and second line conductors.
 4. The invention as defined by claim 3 wherein said at least one YIG resonator is located directly beneath at least one line conductor.
 5. The invention as defined by claim 1 wherein said first and second transmission line means comprise first and second line conductors, and a short circuit conductor contacting said first and second line conductors, said first and second line conductors and said short circuit conductor being located in substantially a common plane on said outer face of said dielectric substrate means, wherein said resonator means comprises a plurality of YIG resonators located in close proximity to said first and second line conductors.
 6. The invention as defined by claim 5 wherein said plurality of YIG resonators are comprised of a first and a second sphere of single crystal yttrium-iron-garnet respectively located beneath said first and second line conductors.
 7. The invention as defined by claim 1 wherein said first and second transmission line means comprise first and second line conductors located in substantially a common plane on said outer face of said dielectric substrate and passing through said dielectric means at a point in proximity to said resonator means and respectively terminating in an electrical short circuit on said outer face of said ground plane.
 8. The invention as defined by claim 7 wherein said resonator means comprises at least one YIG resonator element located in close proximity to said first and second line conductor and said electrical short circuit.
 9. The invention as defined by claim 7 wherein said resonator means comprises a plurality of YIG resonators.
 10. The invention as defined by claim 9 whereiN said plurality of YIG resonators comprises at least three YIG resonators arranged in a row beneath said outer face of said substrate substantially perpendicular to said first and second line conductor and within a boundary defined by said line conductors. 